Comment 3 for bug 1685242
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| Laszlo Ersek (Red Hat) (lersek) wrote | #3 |
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1b1ed1a
(Get the code!)
OVMF places the 64-bit PCI MMIO aperture after the memory hotplug area. If you specify `-m maxmem=1024G`, then accessing 64-bit MMIO BARs of PCI(e) devices, allocated from the aperture, will require at least 41 address bits. If you use KVM, and nested paging (EPT on Intel, NPT on AMD) is enabled, and your /proc/cpuinfo on the host reports a smaller phys address width than 41, then 64-bit PCI MMIO accesses in the guest will silently fail. You can read more details in <https:/
SeaBIOS uses an independent algorithm for aperture placement and BAR allocation.
If you remove virtio-net-pci, then your command line ends up without any PCI(e) device that has a 64-bit MMIO BAR. So the issue is not triggered.
If you use a maxmem of 512G, then 40 bits might suffice. It's possible that your physical CPU has precisely that many address bits, and so the behavior could change.
If you attach the OVMF debug log (capture `-debugcon file:debug.log -global isa-debugcon.
Thus far this ticket looks like "NOTABUG" -- use a smaller memory hotplug area, or disable nested paging (which will come with a performance penalty).